Long-distance electron transfer along redox gradients in the subsurface

Electron transfer (ET) is the fundamental process of life and element
cycling. In the subsurface, the distance of ET determines its influencing
area, normally as short as nanometers or micrometers. Here we provide
direct evidence from column experiments that ET can last over 10 cm along
the redox gradient in sediment columns, through a long-distance ET chain
constituted by a series of short-distance electron hopping reactions
involving with microbes and redox-active species like iron ions (and/or
minerals) and natural organic matters. Microbial processes contribute
largely under biologically active conditions, while chemical processes are
important under extremely acidic/alkaline and cold conditions. Microbial
and chemical processes synergistically mediate the long-distance ET
process, with an estimated electron flux of 6.73 μmol e-/cm2 per day. This
long-distance ET represents an overlooked but important background process
influencing subsurface biogeochemical processes and remediation
activities.